Hyper Extended is a constructed format composed of the black bordered sets from Fallen Empires to Scourge, including the Portal sets One and Second Age and the following promos.
All ante cards are banned.
Hyper Extended features a restricted list (Visual View):
Academy Rector Ancient Tomb Brainstorm Burning Wish Demonic Consultation Earthcraft Enlightened Tutor Frantic Search Goblin Recruiter Memory Jar Mind's Desire Mystical Tutor Necropotence Tinker Tolarian Academy Vampiric Tutor Windfall Yawgmoth's Bargain Yawgmoth's Will
Gold bordered "Championship" cards are permitted, given that they would otherwise be legal in the format. For example, you can use Survival of the Fittest, but you still can't use Birds of Paradise.
Mana burn is on like donkey kong.
Wishes may retrieve cards from your sideboard or exile.
Other modern day rules, such as the London mulligan (the 7-7-7 mulligan), are in effect.
Observe List and Potential Changes
Here's a starter Scryfall search that you can use to check on whether various cards existed during this time period.
game:paper language:english border:black is:booster date>=fem date<=scg